Originally I said there was no mailbox available, but Robert wrote in and mentioned:
Dallas love field does have a mail room located across from restroom near ticket counter.
Robert provided a slice of the terminal map, but I still couldn’t find it on there.
The Terminal Map, small as it is, shows the location of the mail room. It’s identified on the map as item number 4 near the bottom of the map.
It’s pre-security, ground floor (most likely), across from the security checkpoint. There’s a set of bathrooms along the wall. Somewhere around there is the mail room.
This photo from Google Maps is pretty close to where I think it is. The mail room is either around the elevator, or underneath that set of escalators. (You may want to scroll left/right to get a better ID of where it is in the terminal.)
Last updated 23 November 2021